Magnet-core.



J B. SPEED.

MAGNET CORE.

APPLICATION FILED APR. s, 1916.

1,274,952. Patented Aug. 6, 1918.

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//7 van /0/ James 5' (Speed UNITED STATES PATENT OFFIQE.

JAMES BUCKNER SPEED, OF NEW YORK, N. Y., ASSIGNOR T0 WESTERN ELECTRIC COM- PANY, INCORPORATED,-OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

MAGNET-CORE.

To all whom it may concern:

Be it known that I, JAMES BUCKNER SPEED, a citizen of the United States, residing at New York, in the county of New York and State of New York, have invented certain new and useful Improvements in Magnet-Cores, of which the following is a full, clear, concise, and exact description. I

This invention relates to magnet cores generally, and particularly to cores for loading coils for telephone circuits. Its general object is to provide anew and improved core material which is cheap to manufacture, which is easily formed to desired shapes, and which possesses to a high degree those characteristics most advantageous in cores for loading coils and other electrical apparatus.

In loading coil cores the followin characteristics, among others, are desirab e: Mechanically, .the core should be strong enough to stand the stresses imposed upon it in the manufacture of the loading coil; and the core material should be readily formable into any desired shape. It should also be stable as to its chemical composition in spite of age and the changes of temperature to which it may be subjected in service and during the heating processes through which the loading coil passes in the course of manufacture. Electrically, a loading coil core should have high specific resistance; extremely low hysteresis; magnetic stability, that is, should remain constant in permeability as regards talking current even though large currents) are superimposed on the circuit; and should have as high permeability as is consistent with the foregoing desirable electrical characteristics.

Prior to the present invention, loading coils of the most approved forms have been provided with cores made of iron plates or of coils of iron wire Woundito a toroidal' shape. Such cores have been ound to possess the-following limitations and disadvantages, among others: Reduction of eddy current losses beyond a certain value is prevented by the impracticabil'ity of laminating such cores beyond a certain point. Desirable magnetic stability can only be obtained by special and expensive provisions,

such as air-gaps in,the magnetic circuit. Attempts to increase the permeablhty beyond a certain point are. frustrated by ac Specification of Letters Patent.

Patented Aug. 6, 1918.

Application filed April 6, 1916. Serial N 0. 89,409.

companying excessive hysteresis and eddy current losses, and by impairment of magnetic stabilityj The disadvamages and limiting factors ust referred to as inherent in plate and wire cores'are to a great extent avoided by the present invention, which is characterized by the fact that the core is made of finely divided magnetic material which is compressed in a mold by the use of exceedingly high pressure; the individual particles being insulated from one another by a surface coating of some suitable material, such as an oxid of the magnetic material itself. As hereinafter explained, the particles of magnetic-n'iaterial should be fine and soft; and the pressures used in forming the cores should be high enough to distort the particles beyond their elastic limit and to give the core a specific gravity approximating that of the magnetic material employed. The results of such distortion are a reduction in the intrinsic permeability of the particles and an increase in the volume permeability of the core, due to the interknitting of the particles.

It has heretofore been proposed to make magnet cores of iron particles of various sizes usually mixed with a binder and formed to the desired shape in. a mold either with or without pressure. Attempts to make cores in this Way however, particularly cores for loading coils, have been unsuccessful, due, the experiments which led to the present invention seem to indicate, in part to the use of unsuitable iron particles, and especially to the fact that the specific gravities of the cores were far too low, owing to the low molding pressures employed. I

In the drawing, Figure 1 is a perspective view of a section of a loading coil core made in accordance with the present invention; and Fig. 2 shows a plurality of these sections assembled to form a complete core. It will be understood, however, that this is merely illustrative and that the invention is not limited to the production of this form of core, but is adapted for the making of cores of many forms, some of which cannot be made economically .or satisfactorily of solid iron, plates or wires.

In the making of loading coil cores, the present invention is preferably carried out screen. In general, it is satisfactory if all sizes of iron particles small enough to pass through an eighty-mesh screen are used; but

still better cores .may be obtained if only particles of substantially the same size are used, for example, particles which will pass through aneighty-mesh screen and will not pass through a one hundred-mesh screen; This is doubtless due to the fact that when particles of substantially the same size are used, the compression of the compound results in more uniform compression'of the particles and a greater increase in the volume permeability-of the core.

Inorder to provide for the insulation of the particles one from another, said particles are preferably coated with red iron oxid, which is non-magnetic and a good insulating material. The surface of the particles may be oxidized by adding to a mass of the particles approximately ten per cent. by weight of water, and then heating and stirring the mass in the presence of air until dry. The oxid-coated particles are then ready for compression either into bulk material from which 'cores may be made, 01' directly into the desired form of core. The mold and press employed in the compressing process should be-capable of standing and exerting exceedingly high pressures. Preferably, pressures as high as twohundred thousand pounds to the square inchshould be employed; and for the best results as to uniform density, the thickness of any core section, in thedirection in which the pressure is exerted in forming it, should usually not exceed approximately one-quarter of an inch. This consideration is so important that it has been found desirable in making loading coil cores to use coresections even as thin as one-tenth of an inch, and to employ from twelve to fifteen sections in building up a core, a suitable insulating material suchvas paper, lacquer or shellac being interposed between the sections. Fig. 1 shows such a core section or ring; andFig. 2 shows the built-up core.

It has been found that cor'es made in the manner above described are strong mechanically and stable chemically; and that their specific gravity is approximately 7, which is nearly that of undivided iron, which is approximately 7.8. Electrically, a loading coil core of this kind has high specific-resistance, an extremely low hysteresis char,-

acteristic, excellent magneticstability, and comparatively high permeability, as understood in telephone loading coil design. Experiments have shown that better results,

both mechanically and electrically, are obtained from the use of soft rather than hard iron particles; and that the molding pressures employed should be as high as can be obtained. Presumably, this is due to the fact that with soft particles the pressure to which they are subjected strains them beyond their elastic limit and causes them to mesh permanently and closely, thereby permitting the specific gravity of the core to be raised to the high value mentioned. With hard iron particles with either low or high pressures, cores are weak mechanically, perhaps due to the tendency of the particles to return to their original shapes when the pressure is removed, and such cores have a much lower volume permeability than cores manufactured'in the preferred manner described- The volume permeability of a core increases much more rapidly with increase of specific gravity, the more nearly the specific gravity of the core approaches that of undivided iron. In other yvords, increases of pressure are increasingly beneficial as far as volume permeability is concerned eventhough the intrinsic permeability of the particles has been lowered by reason of their compression. It has been found, however, that the tendency of the oxid coatin on the particles to puncture and thereby re uce the resistance of the core section, makes it unwise to use pressures abovea certain maximum value. This value depends, of course, upon the character of the oxid coating on the particles, and in experiments which led to the present invention has beern found to be approximately 200,000 pounds per square inch.

What is claimed is:

1. A magnet core composed of finely divided magnetic material and insulating material separating the particles of magnetic 1 material, the particles of magnetic material being distorted beyond their elastic limit.

2. A magnet core composed of finely di vided magnetic material and insulating material separating theparticles' of magnetic material, said compound having a specific gravity approximating that of the magnetic material employed.

3. A magnet core composed of finely divided magnetic material in the form of particles of substantially the same size, and insulating material separating said particles, said compound having aspecific gravity 'approximating that of the material-employed.

4. A magnet core composed of finely divided magnetic material the particles of which carry a surface oxid, said compound having a specific gravity approximating that of the magnetic materlalemployed.

5. A magnet core composed of finely di which carry a surface oxid of said material, said compound having a specific gravity approximating that of the magnetic material employed.

6. A magnet core composed of finely divided iron and insulating material separating the iron particles, said compound having a specific gravity of approximately 7 y 7. A magnet core composed of finely divided iron, the particles of which carry a surface coating of red iron oxid, said compound having a specific gravity of approximately 7.

8. A loading coil core composed of a plurality of core sections each of which is composed of finely divided magnetic material and insulating material separating the particles of'magnetic material, the compound forming each core section having a specific gravity approximating that of the magnetic material employed.

9. The method of making magnet cores which consists in covering particles of magnetic material with an insulating coating, and forming a mass of said particles into a solid body by pressure sufiicient to distort the magnetic material beyond its elastic limit.

10. The method of making magnet cores which consists in coverin particles of magnetic material with anmsulating coating, and .forming a mass of said particles into a solid body by pressure suflicient to give it a specific gravity approximating that of the magnetic material employed.

11. The method of making magnet cores which consists in covering particles of magnetic material with an insulating oxid, and forming a mass of said particles into a solid body by pressure suflicient to give it a specific gravity approximating-that of the magnetic material employed.

12. The method of making magnet cores which consists in covering particles of iron with a coating of red iron oxid, and forming a mass ofsaid oxid coated particles into a solid body by pressure sufficient to give it a specific gravity approximating that of the iron employed.

In witness whereof, I hereunto subscribe my name this 4th day of April, A. D. 1916.

JAMES BUOKNER SPEED. 

